The present invention relates to a carburetor for a stratified combustion engine with a precombustion chamber.
As an effective method for simultaneously reducing CO, HC and NOx included in exhaust gas from a gasoline engine, it has been theoretically known to supply extremely lean mixture to an engine. However, it has been also known that such lean mixture could not be burnt stably in a conventional gasoline engine because of its poor ignitability and extreme slow combustion rate.
As an internal combustion engine capable of being operated using lean mixture, a stratified combustion engine with a precombustion chamber has been known in the past. A combustion chamber of such an engine consisted of a main combustion chamber and a precombustion chamber communicating with the main combustion chamber through a connecting bore. The combustion in the stratified combustion engine with a precombustion chamber is carried out in the following manner, as has been well known in the art.
After rich mixture has been supplied into the precombustion chamber through a sub-intake valve provided in the precombustion chamber while lean mixture has been supplied into a main combustion chamber through a main intake valve provided in the main combustion chamber, rich mixture in the precombustion chamber is first ignited. Then the flame jets are injected from the precombustion chamber through the connecting bore to the main combustion chamber so that the lean mixture, which would be hardly ignited by conventional combustion system, can be completely burnt by the flame jet without misfire.
Although the stratified combustion engine of the above type has been developed to be put into practice, one of the problems to be solved in the above type of engine resides in the fact that a carburetor of a known type cannot be used with the above type of engine. Thus, although carburetors for exclusive use with the above type of engine have been developed, there are also many problems to be solved in them.
One of the problems involves the structure of the throttle valve actuator mechanism in the carburetor. Particularly, such a carburetor includes a first body having a first bore and a second bore similar to those of a known two-barrel type carburetor as well as a second body having a third body for supplying rich mixture to the precombustion chamber, the bores being provided with a first, a second and a third throttle valves therein, respectively. In the above known carburetor for use with the stratified combustion engine having the precombustion chamber, the first and third throttle valves are mechanically coupled by a link so that when the first throttle valve is swung by an accelerator pedal, the third throttle valve is also swung in accordance with the movement of the first throttle valve. Thus, in a throttle valve actuator mechanism wherein the first throttle valve and the third throttle valve are mechanically coupled by the link, the first bore and the third bore must be positioned in adjacent relationship, which results in an increase of the overall width of the carburetor and brings about an undesirable problem in the design of the engine. In addition, when such a throttle valve actuator mechanism is used, since the third throttle valve is not moved proportionally to the magnitude of a negative pressure within an intake manifold, gaseous mixture of a proper density may occasionally not be supplied to the precombustion chamber through the third bore.